Tucked near Mississippi's border with Louisiana, deep in Entergy Corp.'s territory, rests the largest single-unit U.S. nuclear power station.<p>It's called Grand Gulf, and it boasts a 1,443-megawatt capacity.<p>But it hasn't been acting like a dependable backbone of the power grid.<p>An E&E News review of federal daily reactor status reports from 2013 through last month found Grand Gulf listed at full power roughly 52.5 percent of the time. It was at zero percent power almost 21 percent of the days studied. On other days, it was at various reduced levels.<p>Does that sound like a baseload plant?<p>"No," said Ted Thomas, chairman of the Arkansas Public Service Commission.